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Incremental and Differential Backups - What's the difference?

Views: 20735
Votes: 5
Posted: 11 Sep, 2007
One of the most common questions and confusions that backup admin's have it the difference between incremental backups and differential backups.  The confusion comes because different backup software applications use each term differently.  TOLIS Group, however, uses the term in it's intended form and what an incremental or differential backup was designed to do is the way that all BRU products perform these backup types.  Here's the explanation of each:

Incremental Backups:
An incremental backup is a backup of any file/folder that has changed since the last backup, of any type, was run.  Therefore, if the last backup that ran was three days ago, then the incremental will backups any files that have changed over the past three days.  If the incremental backup is a daily backup, then it will only backup files that have changed since the prior day.

With the incremental backup style, and the example below, the second daily backup does not contain files that have changed for both days 1 and 2, it will only contain file that have changed on day 2.  I'll use dates to better explain this.  If I run a full backup today, August 1, and an incremental backup tomorrow, tomorrows incremental will contain files that have changed on August 2nd.  The incremental that runs on August 3rd (day 3) will ONLY contain files for August 3rd.  It will not contain files from August 1st or 2nd.  Then when the job runs on August 4th, it will contain the files that have changed since August 3rd.  This is because incremental backups only backup the files that have changed since the most recent backup.

Differential Backups:
A differential backup is a backup of any files that have changed since the most recent Full backup.  Using the example below and the date example above, we'll explain this one so that it makes sense.

If you run a Full backup today, August 1st, and daily differentials, then when the differential for August 2nd runs, it will be a backup of any files that have changed since August 1st.  When the same job runs on August 3rd, it will be a backup of all of the data that has changed since August 1st (2 days worth).  Then on August 4th, the backup would contain files from the 2nd, 3rd, and 4th; and so on and so forth.

If you have any further questions about these two backup types, please contact Technical Support.
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